Modern electronic devices provide an increasing amount of functionality with a decreasing size. By continually integrating more and more capabilities within electronic devices, costs are reduced and reliability increased. Touch screens are frequently used in combination with conventional soft displays such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma displays and electroluminescent displays. The touch screens are manufactured as separate devices and mechanically mated to the viewing surfaces of the displays.
Several examples of such touch screens are known, U.S. Patent Publication No. 2002/01759001A1 by Armstrong, published Nov. 28, 2002, describes a touch system for use with an information display system including a frame defining an opening corresponding in size and shape to an information display area of a display. On each side is positioned an array of light-emitting devices with a light-transmissive prism positioned along each array of light-emitting devices such that light emitted from the light-emitting devices is directed across the touch input area. The system also includes light detection devices positioned at each corner of the frame. In a preferred embodiment, the light-emitting devices are organic light-emitting diodes.
U.S. Pat. No. 6,351,260 B1, entitled “User input device for a computer system” filed by Graham et al and issued on Feb. 26, 2002 describes a user input device for an electronic device. The user input device provides positional information using a grid of light. The grid of light is produced from a light source and waveguides. The grid of light is also received and processed using waveguides and a light detector. In this patent, the wave-guides separate light from the light source into a plurality of different light beams that form the grid of light. Light sensors detect when a user positions a finger or other indicator in a location that interrupts the light beams. Optionally, optics may be used to enhance the operation of the user input device.
U.S. Pat. No. 6,181,842, entitled “Position digitizer waveguide array with integrated collimating optics” filed by Francis et al. and issued on Jan. 30, 2001 describes a similar system. In the system of the '842 patent an XY position digitizer is provided that has an X send substrate with an associated X receive substrate, and a Y send substrate with an associated Y receive substrate, defining free space region therebetween. Send waveguides are embedded in the X send substrate and send waveguides are embedded in the Y send substrate. The send waveguides send an array of send light beams across a free space region to the X receive substrate. The send waveguides likewise sends an array of send light beams across the free space region to the Y receive substrate. Receive waveguides are embedded in the X receive substrate and receive waveguides are embedded in the Y receive substrate in correspondence with the X and Y send waveguides. Each receive waveguide receives at least a portion of the light beam from the corresponding send waveguide. An array of X send optical systems are embedded in the X send substrate. One send optical system is in precise optical alignment with each send waveguide for enhancing the collimation of the constrained send light from that aligned send waveguide.
When such touch screens are used with a display, the touch screens are simply placed over the display and the two are held together by a mechanical mounting means such as an enclosure. These prior-art arrangements combining touch screens and displays suffer from a variety of drawbacks. These drawbacks include, but are not limited, to the increased parts count, weight, and cost of the device created by the use of the frame and the presence of redundant components in the display and touch screen. Such prior-art arrangements also increase the thickness of the combination of the touch screen and display as the combination requires that the light sources and light guides project above the surface of the display. Further, there is a risk that the light sources or light receivers can become blocked or contaminated by environmental matter, and thus yield false results. Further, such light guides are capable only of detecting whether a light path has been fully interrupted and are not capable of sensing interruptions in a way that allows for a variable input to be made.
Thus, there remains a need for an improved touch screen and display system that minimizes device weight, removes redundant materials, decreases cost, eliminates special mechanical mounting designs, increases reliability, and minimizes the degradation in image quality.